OVERVIEW
Design The PRO VLA (Vactrol-based Leveling Amplifier) is a multi-purpose tool for audio engineering and recording. Enclosed in a 2U (3.5� high) rack-mountable chassis are two independent channels of analog compression designed to work seamlessly with any recording, sound-reinforcement, or electronic instrument setup. A R T�s PRO VLA circuitry is a hybrid design utilizing the latest and most advanced solid state and tube technology. Using a transformerless design throughout, the PRO VLA maintains exceptional signal integrity and extremely low noise. Its VCAless design utilizes optical electronics (Vactrol) coupled with a 12AX7 vacuum tube gain stage for superior musical performance. The PRO VLA is a soft knee leveling amplifier by design. Although it is capable of providing a thoughougly �squashed� signal, the PRO VLA was designed to excel in areas where transparent, expressively musical dynamics control is desired. Application Compression is used to alter the dynamic range of a signal. In recording and live sound situations, compression and limiting is necessary to manage sounds with wide dynamic ranges. Dynamic Range is measured as the difference between the loudest and softest level of a signal. (i.e. from a scream to a whisper). Once a signal rises above or falls below the set threshold (selectable signal level), the compressor automatically changes its gain to raise or lower the overall signal level. Think of this as manually moving a fader up and down to try to keep a signal at a consistent level. Limiting can be described as a �ceiling�. When using a limiter, once the signal level reaches the threshold, it is unable to go any louder - it is limited to a desired level. In addition to making signal levels more manageable, it is common practice to apply compression or limiting to a signal to make it louder or more �in-your-face�. The benefit of using the PRO VLA for these applications is in its design. By utilizing opto-electronics, the PRO VLA allows you to add more compres-
sion without sounding like you�re squashing the daylights out of the signal. Unlike typical compressors which use VCA�s to control level detection, the PRO VLA is very musical. The nature of its operation is much like the way your eye adjusts to light. Just as your eye transparently adjusts to changes in light, the PRO VLA adjusts to changes in signal level.
SETTING UP
Unpacking Your PRO VLA was packed with care at the factory. The shipping carton was designed to protect it during initial shipment. Please retain this carton for use in transporting the PRO VLA when it is not installed in a rack, or in the unlikely event that you need to return your PRO VLA for servicing. The shipping carton should contain: - The PRO VLA - The owner�s manual - User Registration Card AC Power Hookup The PRO VLA has an internal power supply designed to operate at 100 to 125VAC, 50 to 60Hz. Units manufactured for use outside of the United States of America have been modified to comply with the required electrical specifications. Under no circumstances should the power cable be altered. If the cable becomes cut or damaged, discontinue its use and have it replaced before operating the Pro VLA. Audio Connections Audio connections to and from the PRO VLA are balanced XLR (Pin 2 Hot (+), Pin 3 Cold (-), Pin 1 Ground) and active balanced 1/4� TRS (Tip = Hot (+), Ring = Cold (-), Sleeve = Ground). Unbalanced 1/4� cables may be used with no damage to the PRO VLA. We recommend using only high-quality cables equipped with the appropriate connectors. Installation The PRO VLA may be employed in a number of setups including: - Between a microphone preamplifier and a mixer, digital multi-
